(1) Field of the Invention
The present invention relates to a safety seat belt system for vehicles such as motor vehicles and, more particularly, to a safety seat belt system of the built-in type wherein all the major components of the system are incorporated on or in the vehicle seat itself and which is especially suitable for use with reclining vehicle seats provided with backrests adapted for adjustment of angle.
(2) Description of the Related Art
The various types of safety seat belt systems currently in use include two-point, three-point, and other types. Generally, in these seat belt systems, an end of a seat belt or webbing is securely anchored to a fixed point on the vehicle body, and the other end of the belt is retractably connected to a seat belt retractor to remove unnecessary slack in the seat belt.
Typically, a seat belt retractor comprises an emergency-locking-type retractor (ELR) provided with a retracting reel or shaft adapted to be locked when an emergency situation occurs in which the vehicle is subjected to sudden deceleration or stoppage by collision, and the like. The retracting reel is normally biased in one direction by a helical spring to wind up the seat belt with a relatively small winding force. Namely, when the user pulls the belt, the belt is unwound from the retractor against the action of the helical spring. Conversely, when the user releases the belt, the belt is retracted within the retractor and wound around the reel, to prevent the formation of slack in the belt. This provides the user with an increased flexibility of body movement during normal conditions in the vehicle. In an emergency situation, an inertia element senses any sudden deceleration of the vehicle and triggers a locking mechanism which locks the retracting reel, thereby preventing further unwinding of the seat belt and restraining any involuntary movement by the occupant.
Seat belt retractors of the general concept described above are widely used and are referred to as emergency-locking-type retractors (ELR).
In modern motor vehicles, it is customary to design the seat so that it is adjustable in various dimensions to ensure that the occupant can assume any desired comfortable position. Thus, the backrest of the seat is hinged to the seat cushion, to allow adjustment of the rake or reclining angle of the backrest. In addition, the seat is mounted on a slidable carriage, to allow adjustment of the seat in the fore-and-aft direction with respect to the vehicle floor. In some cases, seat lifting mechanisms are provided to allow adjustment of the height of the seat cushion with respect to the vehicle floor. In such adjustable vehicle seats, it would be a great improvement if all the major components of the seat belt system, such as anchoring members, buckles, tongue plates, and retractors could be incorporated into the seat, so that these components move together with the seat during seat adjustment. Such an improvement would ensure a proper positioning of the seat belt with respect to the occupant, regardless of any changes in the position of the bakcrest and/or the fore-and-aft position of the seat cushion. In this specification, a safety seat belt system having all the major components thereof incorporated on or in the seat will be referred to as a built-in-type seat belt system.
For a built-in type safety seat belt system to be incorporated into a reclining seat, it is desirable to use an ELR in order to provide flexibility of movement for the user. In this case, the ELR may be built-in within the backrest of the seat. However, the conventional ELR is not suitable for such an arrangement because it includes an inertia sensing element in the form of a pendulum weight or an inertial ball, which must be held in a predetermined inoperative position to ensure the proper function of the retractor. Namely, if the angle of the backrest is altered due to adjustment after the ELR is mounted to the backrest, then the pendulum weight will be moved into a non-vertical operative position or a ramped tray supporting the inertial ball will be slanted into an operative position, and thus will incorrectly indicate an emergency situation of the vehicle. For this reason, it has been difficult to combine a reclining seat with a built-in type seat belt system including an ELR.